Not Applicable.
Not Applicable.
Not Applicable.
In general terms, the invention relates to a system and a method for changing the real speed of a work vehicle with a continuously variable transmission and an electronic control device with cruise control function.
A motor vehicle comprising a system of the type mentioned above is known from European Patent EP-A2-0 305 156. With this apparatus, the transmission ratio is controlled in response to the motor load and the desired driving speed in a manner to maintain this driving speed as far as possible.
Further, the general construction and the mode of operation of an example of a cruise control apparatus may be seen from the publication xe2x80x9cVDO Querschnitt 2xe2x80x9d, May 1979 of the company VDO Adolf Schindling AG, Schwalbach, Germany.
The work vehicle may be a construction vehicle, an agricultural vehicle or a municipal vehicle, and the continuously variable transmission may be of any type. As an example and especially, a power distribution transmission having a control in accordance with European Patent EP-A1-0967 107 is taken into consideration.
With continuously variable transmissions for work vehicles, a cruise control function is required to exactly maintain the optimum speed)during lengthy work trips (for instance sweeping, plowing, or mowing). Under these circumstances it is necessary in certain situations to temporarily drive with a different (in most cases, lower) speed and then resume driving with the optimum speed. Such situations may be: turning on the headlands when plowing, where narrow turns have to be made and where it is often necessary to drive back and forth; driving faster over bare areas when mowing; driving downhill with heavy towed loads, wherein possibly the real or actual speed has to be reduced; and, finally, when making an emergency stop. Thereafter, the optimum speed automatically and exactly has to be reached again. It is desirable to be able to memorize also the reduced speed in a reproducible manner.
On making narrow turns, it is necessary and conventional with agricultural tractors to use steering brakes. This term is used for service brake systems that are split up to the brake pedal such that on actuating one half pedal only the wheel on the inner side of the turn is braked. It is, of course, not possible to simultaneously actuate by foot the brake and a further pedal for changing the real speed.
It is therefore an object of the invention to design a system and a method, respectively, of the type set out above in such a manner that all operational requirements mentioned above may be fulfilled, i.e., to provide the cruise control function in an exclusively manually interruptable manner, such that a simple and safe handling of special situations is facilitated.
In accordance with one aspect of the invention, a system for changing the real speed of a work vehicle with a continuously variable transmission and an electronic control device with cruise control function is provided, said system comprising the following operating elements:
a) an actuating element for changing the real speed of the vehicle, said real speed being continuously memorized as a first real speed and being maintained by the cruise control function if no readjustment takes place, and
b) at least one switch for disenabling and re-enabling the cruise control function, wherein the set first real speed is kept memorized on disabling and is set again on re-enabling,
This apparatus is characterized in that a further switch is provided, a speed, especially of zero, corresponding to a standstill of the vehicle, being adjustable by actuation of said further switch, whereupon by means of the actuating element a second real speed is adjustable for the maneuvering travel, said speed increasing up to a predetermined maximum value as long as the actuating element remains activated, and in that by actuating the further switch again, the cruise control function for the first real speed may be re-enabled.
According to an advantageous development, a switch is provided, a second real speed being adjustable and memorizable by means of the actuating element after actuation of said switch, and in that by actuating said switch again, the cruise control function for the first real speed may be re-enabled and the second real speed that was finally adjusted, is memorized.
Said at least one switch may be a switch that permits, after actuation thereof, adjustment of a second real speed by means of the same actuating element. Thus, the switch effects the disenablement of the cruise control function for the first real speed, this speed still being kept memorized, and the adjustment of the second real speed may take place by means of the same actuating element by which also the first speed is adjusted. This constitutes a substantive alleviation of the load and prevents operator errors since the respective finger of the operator may remain at the same customary position for changing the speed. This is a special advantage with turn maneuvers when plowing where in addition to the actuation of the steering, additional control manipulations and the actuation of the steering brake are required.
An ergonomically beneficial arrangement consists in locating the actuating element and the at least one switch on an operating interface within the reach of at least one finger of the operator; in a preferred embodiment, the operating interface being disposed on a stationary control lever within the reach of the thumb and the hand holding the control lever. The combination of control lever and operating interface provides the benefit that the operation of the vehicle is not affected by vibrations thereof. In this manner, an undesired or badly proportioned adjustment of the speed on the occurrence of vibrations of the vehicle is prevented since for the control action a relative movement between the finger and its supported hand is sufficient.
In an especially preferred embodiment, the actuating elements consists of two momentary contact push button switches, one for increasing and one for decreasing the real speed. In combination with the electronic control, it is especially safe and useful to adjust the speeds only by the length of time during which the one or the other of the momentary contact switches is depressed. The adjustment rate of the actuators within the drive train (comprising the drive engine and the continuously variable transmission) then determines the rate of change of the driving speed. A large difference between the desired and real speed is thereby prevented such that the cruise control function is more exact and soft.
According to a further aspect of the invention, a method for changing the real speed of the work vehicle with a continuously variable transmission and an electronic control device with cruise control function is provided that comprises the following steps:
a) a first real speed is adjusted by means of a first actuating element, continuously memorized within the control device and maintained by the cruise control function as long as no readjustment is performed such that the first real speed that was finally adjusted, is kept memorized.
b) the cruise control function for the first real speed is disenabled on actuating a switch, whereupon a second real speed is commanded,
This method is characterized in that said second real speed is a predetermined speed, especially of zero, corresponding to a standstill of the vehicle, in that by means of the actuating element a second real speed is adjusted for the maneuvering travel, said speed increasing up to a predetermined maximum value as long as the actuating element remains activated, and in that for returning from this second real speed to the first real speed memorized in the cruise control function, again a switch is actuated.
Further advantageous embodiments and developments are set out below. They ensure by their sensual perception and full use of the possibilities of an electronic control a maximum of operator convenience and safety. They are the result of detailed studies of movement of the operator.
An especially advantageous method for changing the speed on maneuvering with the assistance of an actuation of the foot brake on one side (steering brakes) and the forward/backward selection lever, comprises the following steps:
a) the vehicle is brought to a standstill by actuating the second switch,
b) by means of the actuating element, a second real speed is adjusted for the maneuvering travel, said speed increasing up to a predetermined maximum value as long as the actuating element remains activated,
c) a narrow turn is made with unilaterally actuated foot brake,
d) the vehicle is brought to a standstill by releasing the actuating element,
e) the forward/backward selection lever is brought into the backward position,
f) the steps b), c) and d) are repeated on driving backwardly, all this repeatedly if required, and
g) by actuating the first switch, the cruise control function for the memorized first real speed is re-enabled.